In a wireless communication system, the Frequency Division Duplex (FDD) mode and the Time Division Duplex (TDD) mode are widely adopted. FDD refers to a mode that different frequency resources are respectively used for Uplink (UL) communication and Downlink (DL) communication. TDD refers to a mode that the same frequency resources are shared by UL and DL communication, and UL communication and DL communication are respectively performed based on time domain division.
For example, a Long Term Evolution (LTE) system corresponding to the Evolved Universal Terrestrial Radio Access (E-UTRA) protocol developed by the 3rd Generation Partnership Project (3GPP) supports two Duplex modes, FDD and TDD. Structure of a radio frame includes structure of a FDD frame and structure of a TDD frame.
Structure of a FDD frame is shown in FIG. 1, a UL radio frame or a DL radio frame with the length of 10 ms is composed of twenty time slots with the length of 0.5 ms and the numbers of 0˜19, the time slot 2i and time slot 2i+1 form a sub-frame with the length of 1 ms, different frequency resources are respectively used in UL communication and DL communication. Structure of a TDD frame is shown in FIG. 2, a radio frame with the length of 10 ms is composed of two half frames with the length of 5 ms, each half frame contains 5 sub-frames with the length of 1 ms. Sub-frame i contains two time slots 2i and 2i+1 with the length of 0.5 ms. The same frequency resources are shared by UL and DL communication, and UL communication and DL communication are respectively performed on different sub-frames of a radio frame.
In above two frame structures, for a normal Cyclic Prefix (CP), one time slot includes 7 symbols with the length of 66.7??m, and the length of the CP of the first symbol is 5.21??m, the length of the CP of any of other 6 symbols is 4.69??m. For an extended CP, one time slot includes 6 symbols, and the length of the CP of each of all symbols is 16.67??m.
UL and DL configuration supported in TDD mode is shown in table 1, for each sub-frame in a radio frame, “D” indicates DL sub-frames, “U” indicates UL sub-frames, and S indicates special sub-frames used for three special domains, a DL Pilot Time Slot (DwPTS), a Guard Partition (GP) and an UL Pilot Time Slot (UpPTS). The lengths of DwPTS and UpPTS are shown in table 2. The lengths of above three special domains satisfies that the total length of DwPTS, GP and UpPTS is 30720·Ts=1 ms. Each sub-frame i is represented by two time slots 2i and 2i+1, the length of each time slot is Tslot=15360·Ts=0.5 ms, the unit of time Ts is defined as Ts=1/(15000×2048).
LTE TDD supports UL and DL switching periods of 5 ms and 10 ms. If the conversion point period from DL to unlink is 5 ms, the special sub-frames exist in two half frames. If the conversion point period from DL to unlink is 10 ms, the special sub-frames only exist in the first half frame. Sub-frame 0, sub-frame 5 and DwPTS are always used for DL transmission. UpPTS and sub-frames following the special sub-frames are dedicated to UL transmission. The configuration in table 1 may flexibly support different asymmetrical services. The special sub-frame configuration in table 2 may support GPs with different lengths, support different cell radius and avoid the strong interference between BSs in the TDD system.
TABLE 1Unlink-DLcon-Unlink-DLfigurationConversionSub-frame numbernumberpoint period012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
TABLE 2Normal CP, DLExtended CP, DLSpecialUpPTSUpPTSsub-frameNormalExtendedNormal CP,Extended CP,configurationDwPTSCP, ULCP, ULDwPTSULUL0 6592 · Ts2192 · Ts2560 · Ts 7680 · Ts2192 · Ts2560 · Ts119760 · Ts20480 · Ts221952 · Ts23040 · Ts324144 · Ts25600 · Ts426336 · Ts 7680 · Ts4384 · Ts5120 · Ts5 6592 · Ts4384 · Ts5120 · Ts20480 · Ts619760 · Ts23040 · Ts7219522 · Ts ———824144 · Ts———
Both TDD mode and FDD mode have its own advantages and disadvantages. For example, the UL and DL configuration shown in FIG. 1 is configurable, and is able to better support the asymmetric service, and increase the usage efficiency of spectrum. When there is more DL services on FDD paired spectrum, the UL spectrum resources will be wasted. However, since the spectrum of FDD is paired spectrum, there are always available UL and DL resources. Thus when a terminal timely feedbacks an UL control single, such as an Acknowledge/Non-Acknowledge (ACK/NACK) message of a Hybrid Automatic Retransmission Request (HARD), and Channel state information (CSI), the feedback delay of air interfaces may be decreased, and scheduling efficiency may be increased. In addition, since the same frequency resources may be shared in TDD system, the channel reciprocity may be achieved, thereby better using smart antennas. Therefore, in the future wireless communication system, if the advantages of both TDD mode and FDD mode may be integrated, and the two duplex modes are capable of being flexibly used or mixed in the light of different scenarios in the same network, the network performance and usage efficiency of spectrum will be greatly improved.